Our present invention relates to a motor-vehicle door lock of the type in which a lock mechanism, usually provided with a locking lever and an electric-motor drive, is electrically energized to displace the mechanism between locked and unlocked positions. In particular, the invention relates to such door locks which may be connected in a central-locking system for the vehicle and which within or at the end of a time interval for an energization which is sufficient to lock or unlock the device, the mechanism has a blocked position at a certain point in time. This point in time, at which the mechanism is mechanically blocked is referred to herein as the blockade time point.
Vehicle-door locks which are motorized and in which the electric motor can be connected via a transmission to an actuator which, in turn, can be coupled with a central locking lever of a mechanism for locking and unlocking the vehicle door, can be electrically energized through a central locking system of the vehicle. A particularly effective vehicle-door lock or latch for that purpose is described in German patent document DE 35 26 501 C2 and U.S. Pat. No. 4,735,447.
The door latch is energized usually for a predetermined time interval which suffices to displace the mechanism between the unlocked and locked position and usually this energization in time is sufficient to compensate for any tolerances or lags in the mechanical system. In other words the blockade time point usually lies within the predetermined time interval.
Usually at the ends of the positions xe2x80x9cunlockedxe2x80x9d and xe2x80x9clockedxe2x80x9d, the latch mechanism engages an abutment. Since the energization of the electric motor of this mechanism can continue beyond engagement with the abutment so that the mechanism largely is at standstill and the mechanism is thus mechanically stressed.
In many cases, the elements of the transmission are composed of synthetic resin materials or are so shaped to bend or compress slightly. The result is an elastic deformation of mechanical parts of the latch which can give rise to a variety of problems.
Where the mechanism is a unit which is connected to the door closure via a rod, lever or linkage, the number of elastic parts in the system is increased.
Since the de-energization of the electric-motor drive usually is incident and the relief of the mechanical stress is abrupt, the elasticity of the system is liberated correspondingly abruptly and can give rise to a movement of parts within a certain play of the system at its bearing and mechanical coupling points which can produce undesirable sounds.
Indeed, two completely separate sounds may be produced in such a latch system. The first sound, which is usually desirable, signals the attainment of an end position, either the blockade instant or the point of engagement with the abutment. However, the second sound, which is produced when the stress is released from the mechanical system is an undesirable sound and may confuse the user. For example, when the first sound signals that the door is latched or locked, the second sound may improperly confuse the user into thinking that the door is unlatched.
It is, therefore, the principal object of the present invention to eliminate this drawback and in particular prevent the sounds associated with the relief of the stresses in the mechanical-latch portions of a motor-vehicle door lock.
Another object of this invention is to so improve the motor-vehicle latch of the type described in the aforementioned patent that detrimental or undesirable sounds as a consequence of elasticity in the drive system can be reliably avoided.
Still another object of this invention is to provide an improved latch system which avoids drawbacks of earlier devices.
These objects and others which will become apparent hereinafter are attained, in accordance with the invention in a motor-vehicle door lock which comprises:
a lock housing;
a lock mechanism in the housing having a central locking lever displaceable between locked and unlocked positions and an actuator mechanically coupled with the lever for displacing same;
an electric motor drive coupled with the actuator and including an electric motor; and
an electric circuit connected with the electric motor for electrically energizing same for a required time interval for displacing the lever between the positions whereby the electric motor drive is blocked at a blocking point in time within or at an end of the time interval, the electric circuit having circuit elements for reducing electrical energization of the motor so that at least one of the torque and speed of the motor is reduced with time along a ramp characteristic.
With the system of the invention, therefore, the electrical energization of the drive and thus the torque and/or speed generated thereby can be reduced along a ramp and not incidentally, suddenly or in a shock-generating manner as has heretofore been the case.
The invention is based upon the fact that the product of the speed and the torque of an electric-motor drive corresponds substantially to the electric power of that motor. A reduction of the torque and/or the speed is thus associated with a reduction in the electric power consumption and vice versa.
When the drive is energized electrically with pulse width modulated electric power, i.e. with current pulses of a predetermined duration and frequency and usually rectangular pulses, it is possible, according to the invention, to operate with a pulse with a modulation duty factor which is reduced from a maximum value to a minimum value along the aforementioned ramp characteristic.
In pulse-width modulation, the pulses are of a duration which bears a ratio to the period of the pulses (determined by the frequency) which can range from 100% (i.e. practically a direct-current signal) to 0% (complete de-energization or 0% current flow). With the invention, the pulse-width modulation duty factor or going ratio, i.e. the ratio of pulse duration to period, can be reduced from a maximum value to a minimum value over the ramp characteristic.
According to a feature of the invention, therefore, this ramp can begin at a predetermined maximum value of the duty factor, for example, 100%, and decrease to a minimum value, (for example, 0%) along a substantially linear or continuous ramp. The duty factor is reduced until blocking of the drive occurs, usually at this minimum value. It is also possible to carry out de-energization of the drive by reducing the duty factor from its maximum value to its minimum value along a plurality of linear ramps, usually at least two and at least two adjoining ramp segments can have different slopes.
The beginning of the ramp can coincide with the blockade time point or can commence at a predetermined interval before this time point.
In all of the cases described, the de-energization of the drive, i.e. the shutdown, takes place cleanly with relief of any mechanical stresses and thereby eliminates the second detrimental noise which has resulted heretofore from abrupt de-energization. The second noise can be completely eliminated when the ramp commences before the blockade time point is reached so that the blockade time point coincides with the minimum value of the ramp or, lies within the ramp so that the ramp does not extend significantly beyond the blockade time point. The circuitry for the purposes described can include semiconductors, usually FET transistors which simply the pulse-width modulation. A conventional microcontroller or microprocessor with appropriate hardware or software (firm wear) can be used to control the FETs and thus to provide linear pulse-width modulation control.
With this system the linear relationship between the motor current or motor power and torque and hence the linear torque increase or decrease can be simply programmed and hence the ramp controlled by the microprocessor. Preferably the pulse-width modulation frequency is 15 kHz or more so that the control operations themselves do not generate any audible sound level.